High strength alloy steel for atmospheric and elevated temperature service



June 4, 1963 p. PAYsoN ETAL 3,092,491

HIGH STRENGTH ALLOY STEEL FOR ATMOSPHERIC AND ELEVATED TEMPERATURE SERVICE PETE/P Bq v soN.

A1. /K/v E.' NEH/PENBERG.

MMMQWJ ATTO NEKS.

June 4, 1963 P. PAYsoN ETAL 3,092,491

HIGH STRENGTH ALLOY STEEL FOR ATMOSPHERIC AND ELEVATED TEMPERATURE SERVICE Filed May 2, 1957 2 Sheets-Sheet 2 A BLYv//v E'. NEHfPE/VBERG.

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ATTORNEYS.

United States Patent O 3,092,491 HIGH STRENGTH ALLQY STEEL FOR ATMOS- PHERIC AND ELEVATED TEMPERATURE SERVICE Peter Payson and Alvin E. Nehrenberg, Pittsburgh, Pa.,

assiguors to Crucible Steel Company of America, Pittsburgh, la., a corporation of New `lersey Filed May 2, 1957, Ser. No. 656,561 3 Claims. (Cl. 75-126) This invention pertains to an alloy steel, of low total alloy content, containing in addition to carbon, as the only essential alloying constituents, manganese, silicon, chromium, vanadium and molybdenum, in critically limited amounts of each and proportions such as to impart to the steel on appropriate heat treatment as set forth below, a tensile strength at room temperature of at least 290,000 p.s.i. and at ll F. `of at least 150,000 p.s.i. together with good tensile elongation and a reduction of area of at least 28% at room and elevated temperatures up to l100 F., said steel being also characterized by excellent toughness and impact resistance at room and elevated temperatures.

There has arisen a need in the aircraft industry for steels of very high strength not only at room temperature but at temperatures as high as 1000 F. or even higher. When aircraft are flown at extremely high speeds 'of the order of Mach 2 to Mach 5, Le., 2 to 5 times the speed of sound, very high temperatures are generated at the surface of the aircraft because of aerodynamic heating. It has been stated that a rough rule for estimating the temperatures generated (measured on the Fahrenheit scale) is to square the Mach number and multiply by 70. Thus for Mach 3, the expected temperature is about 630 F. and for Mach 4, about 1120 F.

Since aircraft must have a minimum of dead Weight, it is necessary that materials of construction have very high strength so that the load carrying section may be reduced to a minimum. For service under appreciable stress at temperatures as high as 1100 F. and higher, the only commercial materials available are the steels, the nickel-base alloys, and the cobalt-base alloys, and of these, the lease expensive, and the most readily available, strategically, are the steels.

It is an object of this invention to provide low alloy steel having very high strength at room temperature and the ability to retain a large portion of this strength at temperatures up to at least 1000 P., such strength to be developed in the steel by a simple heat treatment. It is a further `object of this invention to provide a very high strength steel of relatively low alloy content, free from the strategic elements nickel, cobalt, tungsten, and columbium. It is an additional object of this invention1 to provide a low alloy steel of very high strength which also has adequate ductility, excellent toughness and low notch sensitivity.

Also, because steel of the above-mentioned characteristics has properties desirable for tools for working metals at high temperature, it is a further important object of this invention to provide a low alloy hot work tool steel or excellent toughness Iand relatively low cost.

Since toughness is a very important consideration in the serviceability of a structural steel at a very high strength level, as well as in hot work tools, we limit the carbon in our steel to a level commensurate with a hardness of Rockwell C 52 to C 60. In -a publication by Nehrenberg, Payson and Lillys, Trans. ASM, vol. 47, 1955, page 785, it is shown that steel containing about 3,092,491 Patented June 4, 1963 ICC 0.35 to 0.45% carbon when heat treated to a completely martensitic structure has hardness between about Rockwell C 58 and C 65. We accordingly use a carbon range of 0.35 to 0.45%, and preferably 0.38 to 0.43%, in the steel of this invention.

In order to provide high hardenability in the steel so that parts of relatively small section, for example, sheets for the skin of aircraft, can be hardened adequately, with a minimum of warpage, by an air cool, and so that parts of relatively large section, such as aircraft landing gear as well as tools for hot working applications, can be fully hardened by an oil quench, we use in our steel substantial amounts of the elements manganese, chromium, and molybdenum, which are effective in providing good hardenability in steel.

We limit the manganese to a maximum of about 1% because manganese strongly retards the transformation of austenite and thus a high manganese content makes annealing difficult, and furthermore depresses the Mt` ternperature causing austenite to be retained at r-oom temperature. We limit manganese, therefore, to 0.30 to 1%, and preferably 0.40 to 0.70%.

Chromium and molybdenum are beneficial not only for increasing hardenability but also for causing resistance to softening during tempering. Our investigations have established that steels containing molybdenum as high as 4% are not iappreciably more resistant to tempering than steel con-taining about 2 to 3% molybdenum, as may be seen from the data in Table I below.

TABLE I Eject of Mo on Hardness of Steel After Temperz'ng [All samples heated to 1950 F.-30 min., oil quenched, and tempered 2 hours at temperatures indicated] Composition percent, bal. Fe Rockwell C hardness As tem ered tF. C Mn Sl Cr V Mo As p a quenched We accordingly limit molybdenum to 2 to 3%, preferably 2.2 to 2.8%.

We limit chromium to about 4% on the high side because larger amounts of chromium tend to decrease resistance to softening during tempering. This is shown by the data in Table Il below.

TABLE ll Eyect of Cr on Hardness of Steel After Temperng [All samples heated to 1950 F.-oil quenched, and tempered 2 hours at temperatures indicated] Composition percent, bal. Fe Rockwell C hardness A 0 O Mn Si N1 Or V stempered at F.

AS quenched direction of the test bars.

3 We accordingly limit chromium to 2.5 to 4%, and preferably 3.0 to 3.5%.

Since, as has been shown by Allten and Payson, Trans. ASM, Vol. 45, 1953, page 498, silicon retards softening 4 TABLE Tensile Properties at Temperatures up to 1,100 F. of

Steels of This Invention Compared With Conventional Hot Work Steels Y the longitudinal by tempering in the range of about 400 to 700 F., we 5 I u l h t dt 195m? n h d Th A samp es ea-e o i. o quenc e ose tested atl 000 F. prefer to keep Slhcon m the range of about 5 to 2% and below were tempered2h'ours at 1,000 F.; those tested at 1:100 F. and preferably 0.8 t0 1.5% were tempered 2 hours at 1,100 FJ We have -found that vanadium is very eiective in preventing softening during tempering 4of the `steels of this Steels ofthisinvention Conventional invention in the range 900 to l1l00 F., and we, there- 10 eels fore, use a minimum of about 0.20% in our steel, and 9 a maximum of about 0.5% vanadium, the preferred range Bar 6737 6945 6736 6944 694 5332 being about 0.25 to 0.4% vanadium.

A lthough n mgten is effective in Preventingfteing Rooeiiiiiisim.- 205,000 313,000 310,000 313,000 328,000 204,000 during tempering in the range 900 to ll00 F., it is much 15 Yie1d,1 zpsi 22s, 000 23s, 000 247, 000 24s, 000 232, 000 21s, 000 less eiective in this respect than vanadium. We, thereg'rm' 8'0 70 9'0 8'0 75 '5 fore, do not include tungsten in our steel, except to the 800 een 38.5 31.0 34.0 30.0 23.0 40.5 extent that it may be present as a residual element. Teiche, p si 25e, 000 259, 000 202.000 204,000 270,000 243, 000

it has frequently been stated that nickel in amounts up Yield,l :n.sL-m- 187y 000 202, 000 201.000 220. 000 212. 000 181.000 to about imparts toughness to steel heat treated to 20 nhg'rr n'o 10'5 85 9'0 95 11'5 high strength levels. However, as willi-ie shown below, we 10000 gent 48.5 40.0 41.0 30.0 33.0 50.0

s I have found that our steel containing no more than residual Ter'sue p.s i 228Y 000 2251 000 22J 000 235,000 233,000 214, 000 amounts of nickel, is as tough at high Vstrength levels as eld ansi- E- llifllg 161111108 183.g0g 198.1000.) 103,000 161.g00 steel containing as muchas 2% nickel. Since nickel is Reggerj l 8'5 1 '5 in short supply, We do not specify nickel as an essential 11000 9100--- 42-5 40-0 45.0 36.0 22.0 45.5 ftum mimi d f ,h f siii' ist i033 sin sa 1343s 543g e o n r r i 0.114. r a a p e er e ranges or e Steel o our niongpercen 10. 10.0 12.0 11.5 13.0 15,0

invention are. Red. area, percent 41.5 30.0 48.5 30.0 01.0 50.0

e Of t e above, bars 6737, 694.5, 6736 and 6944 represent this invention; Broad Preferred their analyses are shown in Table I. The other two are conventional hot Work steels which analyze: Carbon.. 38 to .43 vi l. il Eg 1120 Type Bar o Mn si Ni or v Mo W lllckel 1 Ninea 35 rom um. to

HIA 0042 .3s .79 .90 2.15 5.82 .32 3.85 glf 025,(202940 oiirnMow .5332 .33 .4s 1.05 0.11 4.00 1.18 1.14

Norm-Balance iron with usual impurities. 02% Offset Yield Swing?- 40 Percent elongation in 2 ghelaolgahgggson of th resistance to The above data show that the steel of this invention is tempering of a typical steel according to the present irivenraeg tio eagg nllgbangdseo tion versus various commercial grades. In this showing Siderabl Stronper at 11005 F aid is ene'rau s erior tempering temperatures are plotted as abscissae against 4.3 y g g y p Rockwell C hardness Values plotted as ordinates and to the average cost steel at all temperatures and particularly at l100 F as obtained for the various steels over the ran e of tem ering temperatures shown The compositionsgof the stels For a compansonof notcli'sensmmy values at 10000 compared are given in th'e drawing F. of the steels of this invention as compared to the con- FIG 2 is a graphical Comparisn of the tensile Strength 5U ventiilonal steels of Table III, above, 0.357 in. diameter of a typical steel `according to the invention versus-variousV 863206 ifleslrrdlegoxfatgrelxlgc commercial grades over the temperature range extending h 'd. f 0 O 6 from room temperature up to about 1000 F temperanltc lia isblo m" were tested' The data are s ow tures being plotted as abscissae versus corresponding tenthe glertler {aherao oefllgtch sr ltjellngtlhe sile strength values plotted las ordinates. In this figure t th th' 1 th h .o r ns1 also the compositions of the steels compared are shown s feng e ess e non: 'sensmvlty of the Steel (See in the drawing paper by Sachs, Lubahn, and Ebert, Trans. ASM, vol. 33,

1944 afe 340 FIGURE 1 shows that over the tempering range of p o 1000 to 1200D F., the steel of this invention has a better TABLE IV lhdellgrll flytllef 6tlg?)ainesWtl; 69 Comparison of Smooth and Notch Tensile .Strength at 1000 F. steel is inferior to the steel of the invention at temperatures up to ,about 1100 p [Specimens heated at 19.00 F., og quelnehed, and tempered 1000* F.2

ours FIGURE 2 shows that the steel of this invention has much higher tensile strength at all temperatures up to Average Average 1000* F. than any of the kcommercial gradesot high tensile iensiie Ratio, strength steels shown. Bar sniiroeiiiigiiiir nosttgiiedgtiilar ngiircigihto `In the following Table III are shown tensile data over ILS-. 1 psi. n the range extending from room temperature up to 1100 F. for steels of this invention compared with two conventggg gggg 1. 49

.tional hot work steels, one being a relatively expensive ggqg gigjggo j steel containing about 2% nickel and 4% molybdenum, ggg 1. 42 and the other being an average cost steel, the test data 214mg@ 3251000 .being based on measurements made in l Conventional steels.

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These data show that the steel of this invention is less notch-sensitive than the more expensive nickel-bearing steel Bar 6942 and Vonly slightly more notch-sensitive than the average cost steel, Bar 5332.

Further data on relative toughness of the steels of the invention are given in Table V below.

TABLE V V-Notclz Chafpy Tests on Steels Heat Treated to C 55 to 59 Rockwell Thus it is evident that the -steel of this invention is tougher than the nickel-bearing steel, ,and considerably tougher than the higher alloy steels designated B47 and Peerless A.

What is claimed is:

`'1. An alloy steel consisting essentially of about: 0.35 to 0.45% carbon, 0.3 to 1% manganese, 0.5 to 2% silicon, 2.5 to 4% chromium, 2 to 3% molybdenum, 0.1 to 0.5% vanadium, under 0.5% of nickel, balance 4substantially iron, characterized by a tensile strength in the quenched and tempered condition of at least 290,000 p.s.i. at room temperature and at least 150,000 p.s.i. at 1100 F., and by 0 an accompanying reduction of area of at least 28% at room and elevated temperatures up to 1f100 F.

2. An alloy steel consisting essentially of about: 0.38 to 0.43% car-bon, 0.4 to 0.7% manganese, 0.8 to 1.5% silicon, 3 to 3.5% chromium, 2.2 to 2.8% molybdenum, 0.25 to 0.4% vanadium, balance iron except for impurities within commercial tolerances, characterized by a tensile strength in the quenched and tempered condition of at least 290,000 p.s.i. at room temperature and at least 150,000 p.s.i. at 1100 F., and by an accompanying reduction of area of at least 28% at room. and elevated temperatures up to 1100 F.

3. A steel alloy consisting essentially of l0.35% to 0.45% carbon, 0.30% to 0.70% manganese, 0.75% to 1.50% silicon, 3.00% to 4.00% chromium, 2.00% t0 2.50% molybdenum, 0.25% to 0.50% vanadium, and the balance substantially all iron.

References Cited in the file of this patent UNITED STATES PATENTS 1,496,979 Corning June 10, 1924 1,534,473 Taggart Apr. 21, .1925

FOREIGN PATENTS 933,154 Germany Sept. 22, 1955 OTHER REFERENCES 'Tool Steels, pages 269-270. Edited by Gill. Published in 1944 by the American Society for Metals, Cleveland, Ohio. 

1. AN ALLOY STEEL CONSISTING ESSENTIALLY OF ABOUT: 0.35 TO 0.45% CARBON, 0.3 TO 1% MANGANESE, 0.5 TO 2% SILICON, 2.5 TO 4% CHROMIUM, 2 TO 3% MOLYBDENUM, 0.1 TO 0.5% VANADIUM, UNDER 0.5% OF NICKEL, BALANCE SUBSTANTIALLY IRON, CHARACTERIZED BY A TENSILE STRENGTH IN THE QUENCHED AND TEMPERED CONDITION OF AT LEAST 290,000 P.S.I. AT ROOM TEMPERATURE AND AT LEAST 150,000 P.S.I. AT 1100*F., AND BY AN ACCOMPANYING REDUCTION OF AREA OF AT LEAST 28% AT ROOM AND ELEVATED TEMPERATURES UP TO 1100*F. 